Method of and apparatus for removing zinc from copper base alloys



F. FQ POLAND 25429584 Filed Jan. 27, 1944 d '4 sheets-sheet 1 :da /////V/ P n f vw@ ,W im .M m Q Q m W/ Q mw uw N@ oct, 21,1947.

METHOD OF AND APPARATUS FOR REMOVING ZINC -FROM COPPER BASE` ALLOYS v mv sw O Oct. 21, 1947. F. E, POLAND 2,429,584

MTHOD OF AND APPARATUS FOR REMOVINGr ZINC FROM COPPER BASE ALLOYS Filedqan. 27, 1944 4 sheets-sheet 2 mm mw .Mmmm

Oct. 21, 1947. F. F. POLAND 2,429,584

METHOD OF AND APPARATUS FOR REMOYING ZINC FROM COPPER BASEALLOYS Filed Jan. 27f 1944 4 sheets-sheet s Oct. 21, 1947. F. F. POLAND METHOD OF AND APPARATUS EOE REMOVING ZINC ERoM COPPER BASE ALLoYs '4 Sheets-Sheet 4 r u wllllll. A n

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s llllllllllllll It l l l l lllllllll Il Hays Patented Uct. 2l, 1947 METHOD OF AND APPARATUS FOB REMOV- ING ZINC FROM COPPER BASE ALLOYS Frank F. Poland, Rome, N. Y., assigner to Revere Copper and Brassv Incorporated, Rome, N. Y.,

a corporation of Maryland Application January 27, 1944, Serial No. 519,887

(Cl. 'l5-63) 21 Claims.

My invention relates to methods of and apparatus for removing Zinc from copper base alloys containing zinc, so that the nonzinciferous content of the alloy may be recovered, and, if desired, also the zinc content, this application being a continuation in part of my pending applications, Serial No. 429,533, filed February 4, 1942, and Serial No. 484,382, filed April 24, 1943, which latter is a continuation in part of my application Serial No. 429,532, led February 4, 1942.

The invention will be best understood from the following description of several ways of practicing the method and apparatus for use inconnection with such practice, while the scope of the invention will be more particularly pointed out in the appended claims.

In the drawings:

Fig. l is amore or apparatus which may the invention;

Fig. 2 is a longitudinal section of a modied form of apparatus for practising the invention;

Figs. 3 and 4 are sections on the lines -3-3 and rfi-, respectively, of Fig. 2;

5 illustrates a modified form of the metal container of the apparatus according to Figs. 2, 3 and 4;

Fig. 6 is a section on the lined-3 of Fig. 5;

Fig. 'l is a section, corresponding to Fig. 6, showing a further modied form of metal container;

Fig. 8 is a fragmentary view, corresponding to 7, showing a still further modified form of metal container;

Fig. 9 is a section on the line 9-9 of Fig. 8;

Fig. l0 illustrates a further modified form of metal container of the apparatus according to Figs. 2, 3 and 4;

Figs. l1 and 12 are sections on the lines Il-ll and l2-l2, respectively, of Fig. 10; l

13 is a longitudinal vertical section of a modified form of furnace for treating the metal for removing zinc;

Fig. 14 is a longitudinal vertical section of a modified form of apparatus according to Fig. 2;

Fig. 15 is a section on the line 15-15 of Fig. 14;

Fig. 16 is a longitudinal vertical section of a fragment of a modified form of furnace for treating the metal for removing zinc, corresponding to the right nace of Fig. 14;

i7 is a plan of a condenser for the zinc vapors with parts broken away, a fragment of the furnace from which the vapors are received by the condenser being shown; and

less diagrammatic View of be employed in practising hand end of the right hand fur- Fig. 18 is a section on the line lil-i8 of Fig. 17.

Heretofore to recover the copper content of brass, or the non-Zinciferous content of other copper base alloys containing zinc, the metal has commonly been subjected to wasteful and expensive methods of re refining as, for example, blowing the molten metal with air in a reverberatory furnace to oxidize and remove the zinc with resultant loss of the latter.

The attempt to reduce the zinc content of such metal to much under 10% by boiling or evaporating the zinc therefrom has heretofore been commercially, if not technologically, impossible. Heretofore it has been found, that if it is attempted to reduce the zinc content in this way, such high temperature and time are required for removing the final fractions of the Zinc driven oli that the process becomes impractical on account of the high heat energy consumption, lack of durability of the furnace, and time consumed.

in the above connections it will be understood that under constant vapor pressure conditions the minimum temperature at which Zinc will be driven from the metal will progressively increase as the Zinc is progressively removed. Under conditions heretofore prevailing in prior attempts to remove the zinc by heating the metal containing it, the temperature necessary became very high indeed when the Zinc content became small, and when the zinc was reduced to about 3 or 4% resulted in removing the zinc so slowly that reduction in the zinc content practically ceased.

According to the present invention, brass and other copper base alloys containing `Zinc can be commercially .treated to reduce their zinc content readilyto values in the order of 3 to 6%. Further, -by taking advantage of applicants discovery of the catalytic action of incandescent elemental carbon hereinafter explained, the zinc content can be reduced to still lower values, even to fractions well under 1%, that is to say, remove substantially all the zinc without undue consumption of time in the performance of the method, and at temperatures markedly lower than heref toiore has been believed possible, say at temperatures in the order of 1000 F. less than the boiling temperatures determined by Henrys and Raoults laws for metals having the compositions of the final metals. Further, by the improved method the zinc may be recovered in the metallic state, instead of as zinc oxide or blue powder or -be entirely lost as in prior methods.

As illustrative of the catalytic effect oi incandescent elemental carbon above referred to, the

molten metal may be placed in a graphite crucible I (Fig. 1) so as partially to ll it, the crucible being received in the muiie chamber 3 of an oil fired muiile furnace 5 supplied with combustible mixture by the oil combustion nozzle 1. To insure that non-oxidizing conditions exist above the metal in the crucible, a, cover 9 of graphite, or other refractory material, which latter need not be elemental carbon, may be placed upon it, while the mule chamber may be closed by a refractory cover I I, each cover having a small perforation I3 to permit free escape of zinc vapors to the exterior of the furnace, and each cover being sealed with re clay as indicated at I5. Applicant has found that with this apparatus the molten metal may be heated in the incandescent crucible to remove, in several hours, substantially all of the zinc at temperatures markedly lower than the boiling temperatures indicated by the composition of either the original or residual metal. For example, when a molten alloy consisting of 16% zinc, 10% nickel, balance copper was placed in the graphite crucible, which latterI was about 4 inches high, 3.5 inches inside diameter at the top and 3.25 inches inside diameter at the bottom, to fll it to within about 1.8 inches of its top, and the muilie chamber was maintained at about 2850 F. and the interior of the crucible at approximately atmospheric pressure, the alloy at the end of .three hours contained about 0.12% zinc. However, applicant has found that if the crucible, instead of being formed of graphite or other elemental carbon, is formed of other material, then under identical conditions of operation this same alloy will have a residual zinc content of about 2.1%, that is to say, approximately eighteen times as much zinc as that which the residual alloy contains when treated in the graphite crucible.

Crucibles or other containers formed of nongraphitic carbon as, for example, non-graphitic carbon derived from coke, hard coal, petroleum, charcoal, lamp black, etc. will give the same results as a graphite crucible or container, it being possible, when the amount of metal treated in such a container is large enough to constitute practise of the present invention on a, commercial scale, to reduce the amount of zinc in the residual metal to 0.5% and less.

Processes of forming containers, blocks, conduits and various ,other shapes of carbon and graphite arewell known. Commonly according to these processes carbonaceous material, such for example as hard coal, is mixed with coal tar or other suitable binder to form a plastic mass which is molded under pressure to the desired shape, after which the shape is fired to crack and drive 01T the volatile substances and reduce the material to a rather pure form of non-graphitic carbon commercially called carbon By continuing the firing and increasing the temperature of treatment of the shape this so-called carbon may be changed to graphite. The carbon produced is strong, hard and dense, while the graphite while strong and dense is softer adapting it to be more readily machined.

So-called carbon and graphite, aswell as diamonds, constitute the three known allotropic forms of elemental carbon. In the appended claims for convenience of terminology the phrase "elemental carbon is used to indicate material of the group comprising graphite and commercially so-called carbon Diamonds of course, while there is no reason to believe they would be unsatisfactory in an operative sense, are too expensive a material to be availed of in practice.

Crucibles or other containers formed of materials such as magnesite, fire clay, zirconium silicate, silicon carbide, and various other known chemically non-elemental carb on refractories will not give the results obtained with a carbon or graphite crucible, but with them for given temperature and pressure conditions and duration of treatment markedly more Zinc will remain in the alloy being treated, it being necessary with them, if the same residual amount of Zinc is to be secured as with the carbon or graphite crucible and same duration of treatment, to employ undesirable temperatures approximately 1000 F. higher, and commonly with about 3 or 4% zinc as the minimum amount to which the zinc may be reduced if the amount of metal which is treated is large enough to constitute practise of the present invention on a commercial scale.

Applicants explanation of the above eiects is that a molten alloy containing a given amount of zinc has, for a given total vapor pressure, a denite boiling point when placed in a non-carbonaceous container, that is to say, if the alloy is boiled in such a container at a xed temperature and pressure it will continue boiling until the zinc is reduced to a certain percentage amount, and then will cease boiling unless the temperature is raised or pressure reduced to cause it to boil with the reduced amount of zinc, the action being analogous to that which occurs when a mixture of Water and alcohol is heated to boil off the alcohol. However, when a container of elemental carbon is substituted he believes that such material when incandescent acts as a catalyst to reduce the vapor tension at the surface of the molten metal to permit it to boil at a lower ternperature, the same as would occur if the total vapor pressure above the liquid were reduced by use of a vacuum pump assuming it possible to do this. Also it is believed that when the temperature of the molten alloy is below its boiling point for any given total vapor pressure, under which conditions the zinc will evaporate from the alloy if the temperature of the latter is higher than the boiling point corresponding to the then existing partial vapor pressure of the zinc, the same catalytic action occurs, the incandescent elemental carbon then acting to increase the rate of zinc evaporation the same as if the partial vapor pressure of the zinc were much lower than what it actually is. Whatever the correct explanation is, it is nevertheless true that applicant has found that the container of carbon or graphite will act, when incandescent, as a catalyst to cause the amount of zinc in a molten copper base alloy to be reduced by boiling or evaporation at a given temperature and vapor pressure to an amount markedly less than were the crucible not of carbon or graphite and the metal treated in it for the same duration, and further that with a carbon or graphite container the temperature necessary to reduce the zinc to a given percentage amount is markedly less than with a container not of carbon or graphite, and less than that heretofore believed possible or indicated by Henrys and Raoults laws, and that with the carbon or graphite container it is possible to reduce the zinc to a lower percentage amount than were the crucible not of carbon or graphite.

No catalytic effect can be observed when boiling or evaporating commercially pure zinc or copper base alloys containing large amounts of zinc. Under such conditions the zinc boils or evaporates olf so readily from the molten metal, and at temperatures so close to its melting point, that if any catalytic action occurs it cannot be observed and is of no consequence in respect to the results secured under such conditions. Only with about or less zinc can the catalytic action be observed and is of importance.

Thecatalytic effect and its advantages are most pronounced, and become of progressively increas-. ing importance, as the Zinc content isy progressively reduced below 10%. As the zinc content of the brass or other copper base alloy is progressively reduced below 10%, the temperature and time of treatment necessary to evaporate or boil olf a given amount of zinc at a given vapor pressure progressively increase, and, as the catalytic action reduces this necessary temperature and time, taking advantage of that action effects both a marked saving in energy consumption and durability of the furnace while at the same time permitting a greater amount of metal to be treated in a given time.

So far as applicant has found it is necessary, to secure the above described catalytic action, to have a free surface of the body of molten metal being treated, whether that body is in the form of a molten stream or is stationary, so as tc permit the escape therefrom of Zinc vapors,y and to have the elemental carbon intersect that surface in the general sense that the inner surfaces of the side walls of a container of the metal intersect such surface. Further, it is necessary to securing such action to heat the molten metal under substantially non-oxidizing conditions in respect to that metal. Still further, it has been found that the catalytic action is most pronounced when the temperature of the molten alloy being treated is at least that of the melting point of its nonnzincib erous content, which it will ybe understood will be abovethat of the melting point ofY the alloy. Any temperature above the melting point of the non-zinciferous content up to that which causes the alloy to boil may be employed. In practice, to secure best results, temperatures of from 9011 to 140i0 F. above the melting point of the non zinciferous content are preferably employed,` parn ticularly when removing the final fractions of the Zinc if reduced to as low as about 3%.

As to the above, it has been found that the catalytic action willV not take place if the elemental carbon contacts with the molten metal below its surface level only. For example, if the Crucible orv other container is not of carbon or graphite, for example silicon carbide, and the elemental carbon is in the form of a block of graphite or carbon placed in the crucible and xed to its bottoni so as to be wholly submerged in the molten meta-1 no catalytic action will take place andthe resultsl secured will be identical with those secured when the block is of silicon carbide or other material not elemental carbon, whereasv when the block is of elemental carbon and is so fixed in the cru-cible of material other than elemental carbon that it projects from below to above the free metal surface, so as to intersect that surface, the catalytic action will take place.

As an example of a convenient form of apparan for practising the invention on a commercial scale, the molten metal may be `heated in the graphite or hard carbon container i1 constituting the hearth of an eiectric furnace in which the upper free surface i!! of the molten'rnetal is intersected by the inner sides of the side walls 2l and 23 of the container. As shown, the container lll is supported by refractory blocks 25 resting upon the refractory lined bottom wall 21 of a furnace chamber 2a, the side and end walls 3l of the furnace being similarly lined with refractory material. AS shown, at opposite sides of the container I1 the furnace is interiorly formed with a shelf upon which rests a layer of refractory insulating material 33 which supports the electric resistance heating elements 35 extending transversely across and above the container. These resistance elements, which may be formed of graphite, are shown as connected in series by electrically conductive graphite plates 31 resting upon the insulating layers 33, the end resistance elements having extensions I39 of refractory conductive material extending through perforations` il in the furnace wall to the exterior of the furnace where they carry terminals 43 for connection to the source of current. Above the resistance elements is shown a wall 45 of plates of refractory material which in operation are heated by the resistance elements to incandescence and reflect heat downward so as to augment the heating effect on the metal in the container I1. Upon this wall may rest a layer 41 of broken charcoal to act as an insulator for keeping the wall d5 at a maximum temperature.

The refractory linings 25 and 3| and the wall 45 may be of graphite or hard carbon to aid in insuring that non-oxidizing conditions will exist in the furnace, and to this saine end the removable cover 49 of the furnace is shown as provided with a metal casing 5l which coacts with a metal casing 53 for the lower portion of the furnace to form a liquid seal divice 55 extending enrely around the furnace.

Molten metal may be entered into the container l1 from a separate melting furnace 51 through a pipe or other conduit 59 of refractory material such as carbon or silicon carbide, the inner end of which pipe terminates above one end of the container so as to discharge the molten metal into that end. The molten metal may ow from the opposite end of the container through a pipe 61 the bore of which is positioned sufficiently above the bottom of the container to maintain a pool of metal of the requisite depth in the container. From the pipe 6l the metal discharges into a pot s3 of suitable refractory material, from which pot it may be tapped from time to time through the pipe 65 of refractory material normally closed by a removable re clay plug 61. The Zinc vapors may be discharged from the furnace chamber 2.9 through an outlet pipe G9 leading to any convenient place of zinc vapor disposal as, for example, a zinc condenser.

It is possible however to melt the alloy in the i same furnace as that which contains the conthe discharge end of the container.

tainer or hearth l1, for example, as shown in applicants pending application Serial No. 429,533, lecl February 4, 1942, and, if desired, the container I1 may be identical with that shown and described in said application.

As shown, the container or hearth l1 is so designed as to cause the body of molten metal therein in relation to its volume to be of fairly shallow depth and present a large free surface,

so as to facilitate heating of the metal and the escape of Zinc therefrom during its flow through the container. As shown herein, the container is elongated in the direction of the flow of metal through it, which is of advantage in that it acts to promote a progressive rise in the temperature of the metal as the Zinc is removed so as to facilitate reducing to a minimum the amount of zinc in the final fractions of the metal adjacent However,

7 With containers or hearths of rather large capacity, such construction involves complexities in furnace design, to avoid which the container may be made much wider in relation to its length than shown in the drawings without material disadvantage.

The melting furnace, which need be operated only at suflicient temperature to melt the metal, that is to say at a temperature much less than that to which it is necessary to heat the molten metal in the container 1, may be of any suitable sort, that illustrated being an electric furnace having the melting pot 1| of suitable refractory material, above which pot is positioned a pair of resistance heating elements 13. The construction of the melting furnace in respect to the resistance elements and their support may be identical with that described in connection with the other furnace, the resistance elements 13, like the resistance elements 35, being connected at one end by a conductive plate 15 similar to the plates 31 heretofore referred to, which plate 15 rests upon an insulating shelf 33 at the side of the furnace chamber as hereinbefore explained, While each resistance element 13 may have an extension lea-ding to the exterior of the furnace sirnilar to the extensions 39 of the resistance elements 35. Also the melting furnace chamber, like the chamber for receiving the container |1, may have the refractory lining 21, 3|, while the removable cover 11 of the melting furnace includes a graphite block 19 which, like the wall 45 of the other furnace, is heated by the resistance elements and acts to reflect the heat downward toward the metal being treated.

As shown, one side wall of the melting pot has formed in it a vertically extending passage 8| which communicates with the lower interior portion of the pot through a port 83, the pipe 59 communicating with the passage 8| adjacent the normal level 85 of the molten metal in the pot. By this construction assurance is had that slag or dross will in effect be skimmed from the molten metal and not enter the pipe 59. Accumulated slag and dross may be tapped from the pot from time to time through the pipe 81 normally closed by a removable fire clay plug 89.

Metal to be molten may be entered into the pot through the charging conduit 9| which, as shown, communicates with a screw conveyor 93 for receiving scrap metal from the hopper 95. The screw may be rotated through the power driven sprocket wheel 91 continuously or intermittently. As shown, the conduit 9| is provided with a, gate valve 99 which when closed prevents entrance of air into the melting chamber, as does substantially likewise the mass of scrap which normally lls the conduit even when the valve is open. As solid metal is charged into the pot it displaces metal therein and causes it to flow therefrom through the pipe 59 into the container I1. By regulating the rate off feeding the solid metal the rate of supply of molten metal to the container |1 may be regulated within the limits of melting capacity of the melting furnace.

In the apparatus described the molten alloy preferably is heated in the melting furnace to a temperature only slightly above its melting point Aso as to prevent material escape of zinc in the melting furnace, any slight amount of zinc which escapes being vented olf by a vent (not shown) similar to the vent 69 of Figs. 2 and 3. At that temperature it is entered into the preheated container |1 and quickly heated 8 to the temperature desired for removing the zinc. As it passes through the container its temperature is gradually raised and its zinc content progressively reduced until at the discharge port of the container its temperature is at a maximum and its zinc content at a minimum. As the zinc escapes from the surface of the bath the density of the metal from which it is removed is increased, causing that metal to sink, with the result that the surface of the bath at any given point is constantly replenished with the metal richest in zinc at that point, thus facilitating rapid removal of the zinc.

In addition to the carbonaceous material of the container or hearth I1 provided by its edge walls, further carbonaceous material intersecting the free surface of the molten metal in the container may be provided by the upstanding ribs |03 formed integrally with the container bottom as shown in Figs. 5 and'6. If desired, only the ribs |03 may be formed of carbonaceous material, for example graphite or hard carbon, and the remainder of the container formed of noncarbonaceous refractory material, such as magnesite, zirconium silicate, silicon carbide, or the like, in which case the lower edge portions of the ribs |03 may be molded into the bottom wall of the container |1 during fabrication of the container. The ribs in this case may take the form of those shown at |05 (Fig. 7) which may Ibe like the ribs |03 in all respects except that their longitudinally extending lower edge portions |01 are of dovetail shape in cross-section to cause them to be securely locked to the material of the bottom wall of the container. Likewise when the container |1 is of non-carbonaceous material the side and end walls may be provided with inserts |09 of carbonaceous material, such as graphite, as shown in Figs. 8 and 9, so that the exposed surfaces of these inserts will intersect the free surface of the molten metal of the container. The inserts |09 may be of dovetail shape in horizontal cross-section so as to cause them to be locked to the material of the side and end walls of the container when that material is molded about them duringfabrication of the container.

A further form of container or hearth is shown in Figs. 10, 11 and 12. As illustrated in these figures, formed integrally with the side walls 2| and bottom of the container are spaced, transversely extending partitions the opposite ends of adjacent partitions respectively being cut away throughout their entire height to form openings ||3. This construction provides a tortuous passage for the molten metal, the passage consisting of parallel channels ||5 extending transversely of the container and connected at their opposite ends in series by the openings 3. As illustrated, in each channel ||5 is a partition or darn ||1 which extends from one side wall 2| of the container to the other integrally therewith and the container bottom, the tops of these dams being positioned to lie slightly below the upper free surface I9 (Fig. 2) of the molten metal within the container. With this construction the molten meal flowing through the container travels in a tortuous stream back and forth across the hearth through the channels ||5 between the higher partitions and that which enters a given channel ||5 through the adjacent opening i3 must flow over the lower partition or dam 1 to dischargethrough the opening ||3 at the opposite end of the channel. This causes the molten metal to flow in a relatively long path through the container, and also causes turbulence in the flowing stream and thus acts to facilitate evaporation of the zinc by constantly replenishing the surface portions of the metal with metal richer in zinc as the zinc evaporates from these sur-'- face portions.

Other forms of container or hearth may be substituted for those above described as, for example, the higher partitions I I of Figs. 10, 11 and 12 could be omitted while retaining the lower partitions or dams III, causing the container to take the form of a riffle board.

As illustrated, the furnace in which the molten metal is heated to remove the zinc is provided with pipes IIS of refractory material which may be supplied With an inert gas, such as nitrogen or hydrogen, from the communicating pipe |2| leading from a source of supply of said gas, which gas is preferably preheated. Controlled amounts of gas, regulated by the valves |23, may be entered into the furnace chamber from the pipes I I9 so as to sweep across the surface of the molten metal in the container Il and mix with the Zinc vapors to dilute them prior to their passing out the vapor discharge conduit 69. Such a gas will not only aid in insuring non-oxidizing conditions in the furnace chamber, which conditions if they exist it has been found will act to diminish the catalytic effect of the carbonaceous material of the container Il, but will also reduce the partial vapor pressure of the Zinc and thus promote boiling or evaporation of the latter from the alloy whether the container is of carbonaceous material or not. Preferably the chamber is maintained at slightly above atmospheric pressure further to insure the presence of non-oxidizing conditions therein, but the decrease in the rate at which zinc is given olf tended to be caused by this increase in pressure is more than compensated for by the reduction in the partial vapor pressure of the zinc caused by the gas admitted to the chamber through the pipes I9.

With the apparatus shown, the gas thus admitted will be particularly effective adjacent the discharge end portion of the container II, Where the metal contains the minimum amount of zinc. At that portion the rate of Zinc removal from the metal is less than at points toward the opposite end portions of the container. Because of that, and the zinc vapor discharge from the furnace chamber being positioned adjacent such opposite end, the zinc vapors are more dilute and the partial pressure of the zinc vapors consequently less adjacent the discharge end portion of the container.

As shown, communicating with the pipe |2| are further pipes |25 controlled by valves |21, which pipes are preferably formed ofr graphite. The pipes extend through the furnace Wall and discharge into the pot 53 adjacent its bottom. Through these pipes controlled amounts of preheated non-oxidizing gas, hereinbefore referred to, may be entered into the metal in the pot 63 so as to bubble through said metal andl remove residual zinc therefrom. It will be understood that a bubble of gas entered into the metal in this way expands as it rises and forms a space into which the Zinc may evaporate. The gas bubble discharging from the surface of the metal has mixed with it the Zinc vapor which has been evaporated. It then mixes with the gas discharged through the pipes I9 so as to sweep over the surface of the metal in the container I'I.

It will be understood, that where the molten metal' introduced into the container l1 contains large amounts of zinc, the percentage amount of the Zinc in the metal will be quickly reduced to such amount as permits the above mentioned catalytic action to take place. In fact zinc base alloys containing.l sumciently large amounts of copper to warrant recovery of the latter will be quickly reduced, by removal of the zinc, to copper base alloys whether the container "Il is of elemental carbon or not, and consequently in the appended claims by copper base alloys is included metal from which enough zinc is removed during the course of the treatment to cause the metal to become predominantly copper, so that when this occurs the treatment will then remove zinc from a copper base alloy.

It has been found that the initial amounts of c'rre given. off from the metal being treated are evolved very rapidly, and that most of the treatment consists in removing the final fractions of the zinc, and, that independently of the Zinc content of the brass` or other Zinc base alloy entered into the container i'l, the same treatment will reduce the amount of zinc to roughly the same amount so long as that treatment is continued for several hours.

It will be understood that the hearth on which the molten metal is treated for removing the zinc need not be in the form of a container separate from the furnace walls. For example, the furnace may be constructed as town in Fig. i3, according to which the conduit 59 discharges the molten metal from the melting furnace directly on the furnace oor so that the latter and the adjacent portions of the side walls of the :furnace chamber constitute a hearth and the furnace chamber constitutes a container for the metal. In this case' the four lateral Walls 3| of the furnace chamber, and preferably also its bottom walll are formed of a lining of graphite or carbon to secure the abovementioned catalytic effect, while a dam |229 extending entirely across the furnace chamber is provided adjacent the pot i3 to maintain a pool of metal on 'the .furnace floor, the pipe t`-| acting to discharge metal from the pool into the pot 53.

In order to secure better control of rate of treatment of the metal when the furnaces are of relatively large capacity the apparatus preferably employed in such case is that illustrated in Figs. 14. and 15, or the same as modified as indicated in Fig. 16.

As shown in Fig. i6', the melting furnace iii and furnace |33 in which themetal .is treated for removing the zin'c are of similar construction so as to maintain in each a rela-tively shallow pool cf metal having an upper free surface at the level |35. Each furnace, like those heretofore described', is provided' with the removable cover |19 and' heating resistors S5, the latter being arranged and supported as hereinbefore described, while the bottom` and four lateral walls of each furnace are' lined with suitable refractory materiali, such material for the furnace |33' preferab'ly being graphite or carbon for reasons h'ereinbefore4 explained. For charging scrap into the melting furnace ISI' the latter, as shown, is provided with an extension |31 formed with an open ended passage I3@ leading from the eX- teri'or of the furnaceY to the furnace chamber. This` passage is shown as provided with a pair of spaced vertically movable valves or gates IlII formed of refractorymaterial, air cylinders |43 of known construction being provided for independent-ly raising and lowering the gates at the will of the operator. Adjacent the exterior end of the passage |39 is shown a table or other support |45 upon which may be placedbales B of scrap to be slid from the table into the passage. By raising the outer gate |11! a bale may be pushed from the table to position it in the passage |39 in the space between the two gates, whereupon the outer gate may be closed and the inner gate raised, then by means of a bar entered through a notch |41 in the bottom edge of the outer gate the bale may be pushed entirely through the passage into the furnace chamber. As shown, a, valve controlled pipe |49 is provided for conducting an inert gas, such as nitrogen, into the space in the passage |39 between the two gates |4|. This gas is admitted to the passage in such amount, and preferably continuously, as to prevent entrance of air through the passage into the furnace chamber.

The melting chamber of the furnace |3| at its end opposite the charging passage |39 is shown as provided with a block |5| of refractory material, which block is provided with a vertical passage |53 communicating at its lower end with the furnace chamber through a port |55. Communicating with the vertical passage |53 is a downwardly inclined tube |31 of refractory material for discharging molten metal from the furnace |3| to the furnace chamber of the furnace |33. The block 5|, it will be observed, thus acts as a bale or skimmer to prevent dross, slag or the like floating on the surface of the molten metal in the furnace from entering the furnace |33.

The end of the tube |51 projecting into the furnace chamber of the furnace 33 is shown as provided with a downwardly projecting portion |59 extending into the chamber of a cup-shaped block. |6| so that the open end of the tube is submerged in this chamber, from which latter the metal flows over the rim of the cup into the body of the furnace chamber. By this construction the molten metal in the cup seals the adjacent end of the tube against escape therethrough of zinc vapors from the furnace |33 to the furnace |3|, permitting the furnace |33 to be operated at a pressure slightly above atmospheric so as to insure against entrance of air into its furnace chamber and to force the Zinc vapors through the pipe 69 into the Zinc condenser org other place of zinc vapor disposal.

In its form shown by Fig. 14 the metal may be tapped from time to time from the furnace |33 through a pipe |63 of refractory material normally closed by a removable re clay plug |55.

In its modified form shown by Fig. 16 the furnace |33 is arranged for automatically discharging the molten metal at the same rate at which scrap is charged into the furnace |3l. As illustrated in this gure, an open metal discharge pipe |53 extends through the furnace wall from the exterior of the furnace into a block |61 of refractory material positioned at the end of the furnace chamber opposite the metal inlet tube |51. This block, as shown, is formed with an inverted U-shaped passage |69, the pipe |63 communicating with one leg of this passage, while the lower end of its other leg communicates with the furnace chamber adjacent the furnace chamber floor through a port formed in the block. In this way the material of the block between the two legs of the inverted U-shaped passage forms adam which determines the normal level of the upper surface of the metal in the 12 furnace chamber, while the molten metal in the leg of the U with which the port |10 communicates acts to seal that chamber against escape therefrom of zinc vapors through the pipe |63 and insures against entrance of exterior air to the chamber by way of the pipe.

When treating metal which flows sluggishly, as for example alloys containing ponderable amounts of nickel, it in many instances may be desirable to heat the tube discharging molten metal from the melting furnace to that in which the metal is treated for removing zinc, and particularly when this tube is of considerable length. For example, the tube |51 of Fig. 14 may pass through a heating chamber |1| provided with an oil burner nozzle |12 for projecting a flame thereinto for highly heating the tube, the products of combustion escaping from the chamber to a stack |13. In this way assurance will be had against deleterious cooling of the metal in the tube, which cooling if it occurs may cause the metal to flow through the tube with insumcient freedom.

Instead of causing the molten metal to flow slowly and continuously from the melting furnace into the furnace for removing the zinc, the molten metal may be rapidly poured into the last mentioned furnace to charge it to capacity,

and the metal so charged treated for removing the zinc, after which the residual treated metal may be drawn olf and the charging operation repeated to treat a new batch of molten metal. This variant of the method, although resulting in a reduced over-all capacity of the plant, may nevertheless be desirable in some instances, particularly when the metal treated is such as flows sluggishly. In performing the method in this way molten metal may be drawn from the melting furnace into a suitable ladle, preferably one `with a so-called teapot spout, so that upon tilting the ladle metal may be poured through the spout from beneath the upper surface of the metal in the ladle, on which surface may be maintained a layer of powdered charcoal or other suitable material for preventing oxidation of the metal. In such case the furnace for treating the molten metal may be provided with a charging opening into which the molten metal may be poured from the ladle as, for example, the tube |51 of Fig. 14, instead of being connected to the melting furnace |3I, may terminate exteriorly of the furnace |33 and be provided with a suitable funnel for receiving the metal poured from the ladle.

In the above examples the zinc vapors evolved may be conducted to a zinc condenser, in which by cooling the vapors to just below the dew point with respect to zinc they will condense as liquid zinc. It has been found, however, that when an inert gas is entered into the furnace in which Zinc vapors are evolved, the amount of gas entered should be so controlled that the dilution of the incoming gaseous mixture to the condenser is not greater than that which corresponds to a dilution of about 50% by volume at 2000c F., as otherwise the zinc will not be condensed out of the dilute vapors predominantly as liquid zinc. By cooling this mixture in the condenser to just below its dew point in respect to zinc, the zinc will condense out, which dew point will depend upon thedegree of dilution of the Zinc vapors, `while the dilution will increase as the zinc is progressively condensed out. With no dilution or with dilutions up to about 5% the zinc will begin to condense out at about 1700 F., and with greater dilutions at lower temperatures. By designing and operating the condenser to cool the zinc vapors progressively down to about 900". F. as the vapors flow through it, practically all the zinc vapors will be condensed independently of the dilution or temperature of the incoming vapors to the condenser. However, with a dilution of the incoming vapors greater than about 50%, it has been found that the Zinc will condense wholly or in large part in the form of so-called blue powder, which latter does not melt when it falls into any liquid zinc which may be collected in the condenser, and for that reason its presence is objectionable.

The zinc vapors, or mixture of zinc vapors and gas, discharged through the conduit 69 may lead to the Zinc condenser more or less schematically shown in Figs. 17 and 18. Such condenser comprises the upper and lower headers VM and |15 lined with refractory material and connected by vertical tubes il? of refractory material of good heat conductivity such as graphitic fire clay. As shown, the conduit 69 communicates with the lower header, from which latter the vapors rise through the tubes Vil to the Aupper header, the latter being provided with a vent pipe |19 controlled by a valve I3 i. Arranged about each tube are vertical pipes |83, each provided with jet nozzles 85 for playing a gas fiame against the tubes. As shown, these pipes are supplied with fuel gas from a header |81, each through a carburetor |89 of known construction for mixing the gas with air so that the gas burner is of the Bunsen type. Valves |91 for manually controlling the amount of gas supplied the carburetors are provided for regulating the fla-me. The* flame is so regulated as to cause the tubes gradually to cool the vapors ascending through them to just below the dew point of the vapors with respect to Zinc so that the zinc condenses out in liquid form and rains downward through the tubes into the lower header |15. Any zinc which condenses in the upper header will drain therefrom down the tubes into the lower header. The lower header, as shown, is provided with a discharge tube |93, normally closed by the removable fire clay plug |95, for tapping the molten zinc from `time to time, the zinc in this header being maintained in molten condition by the vapors from the furnace passing over that metal.

It will be understood that the valve |8| in the vent pipe |19 from the upper header |14 of the condenser may be manually adjusted to regulate the pressure in the chamber of the furnace in which the molten metal is treated for removing the Zinc. If desired, however, the valve may be automatically regulated in a lrnownV manner in response to the pressure in the furnace chamber to maintain that pressure at a predetermined constant value.

Preferably, as above explained, each of the several melting furnaces described is also provided with a vent pipe, such as the conduit 69 of the furnace i3! of Fig. 14, for escape of any zinc vapors unavoidably generated in that furnace. Commonly the amount of zinc vapors generated in the melting furnace will be small, for example, not exceeding about of the total Zinc when the zinc content of the alloy charged is about 16%. rllhe amount of zinc vapors however will vary with the percentage amount of zinc in the alloy charged, and with alloys of high Zinc content, for example Muntz metal and Admiralty metal, may constitute a fraction of the Zinc of economic importance. For this reason the vapor vent pipe for the melting furnace preferably leads to a zinc condenser` which may be identical in construction and operation with that above described except that it need not be of as large capacity.

As an example of the practice of the method, but without limitation thereto, and assuming the apparatus according to Fig. le is employed, the furnace chambers of both furnaces i3i and |33 may be interiorly 9 feet long and 411/3 feet wide at the furnace floor, each furnace being lined with carbon and being designed to have a capacity Vof about 5 tons of metal corresponding to a pool of metal therein about 6 inches deep. In each furnace six graphite resistor bars 35 about 6 inches in diameter and 4 feet long may be employed, their axes being positioned about 25 inches above the furnace oor in the case of ythe melting furnace |3| and 16 inches in the case of the furnace 133. Assuming the furnace |33 is arranged for non-continuous discharge as shown by Fig. 14, and the scrap is an alloy consisting of 16% zinc, 10% nickel, balance copper, bales B of the scrap may be fed to the melting furnace |3| until that furnace is full of molten metal and the latter is about to overflow into the furnace |33. Thereupon the bales of scrap weighing 40 pounds each may be fed at the rate of one bale per minute, in other words, at the rate of one ton per` hour, for about 5 hours until the furnace |33 is filled with molten metal to the .above mentioned depth, whereupon the charging of the scrap may be discontinued. Under these conditions sufficient current may be passed through the resistors of the furnace |35 to melt the scrap and cause it to be discharged from that furnace into the furnace |33 at a temperature of about 2100 F., which is slightly above its melting point, while sufficient current may be passed through the resistors of the furnace |33 to heat the metal to a temperature of about 3000" F. 1f after the furnace |33 is charged in this way the treatment is continued at 3000 F. for one hour to cause the average time of treatment of the metal charged in that furnace to be about 3.5 hours the zinc content of the metal will be reduced to about 2.5%, without at any time entering nitrogen or the like into the furnace. On the other hand, by continuing the treatment so that the Vaverage time of i'freating` the metal charged -i-n the furnace is about 8 hours the zinc content will ybe reduced to about 0.5%. Were a lining of ma* terial other than `elemental carbon employed in the furnace |33 the zinc content would be reduced only to about 6% instead of 2.5% in the first example of time of treatment, Vand only to about 3.5% instead of 0.5% in the second example. By entering controlled amounts of nitrogen or the like the time of treatment'necessary to reduce the zinc content to a given amount may be reduced as much as 25% in each example, this reduction being true where an elemental carbon or other lining for the'ful'nacei is =em ployed. After the metal is treated in the furnace |33 as just described it may be tapped to empty that furnace, whereupon the charging of scrap to the full furnace |3| may be recommenced to repeat the operation. When the furnace |33 is -arranged `for continuous operation, as shown in Fig, 16, the chargingcf the melting furnace i3! may be continued indefinitely without interrup tion, the metal being passed through the furnaces at the desired rate to esecure the` required reduction in zinc content. For example, passm ing an alloy :of the 'composition mentioned through furnaces of the dimensions mentioned, maintained at the temperatures mentioned, at the rate of about 1.1 ton per hour determined by the rate of feeding solid alloy to the furnace |3| will treat the metal in the furnace |33 for about 3.5-hours and reduce the zinc content of the metal discharged from the furnace |33 to about 2.5%, while treating it at about half that rate will reduce its Zinc content to about 0.5%, in each case Without entering nitrogen into the furnace |33, and these times may be reduced about 25% by entering proper amounts of nitrogen into the last mentioned furnace.

In the above mentioned specific examples of the practice of the method the condenser employed for reducing the zinc vapors to the metallic state may be in the form shown in Figs. 17 and 18 employing tubes |11 about 6 inches inside diameter and about 31/2 feet long with walls about 3A of an inch thick formed of a mixture of graphite and fire clay, two such tubes being employed for the condenser for the vapors from the melting furnace 3| and four for the condenser for the vapors from the furnace |33. In practice, assuming the alloy being melted contains about 16% zinc, about 5% of the total zinc charged to the melting furnace Will be recovered in the condenser associated with that furnace, While the remainder, less that contained in the nal metal, will be recovered in the condenser associated With the furnace |33.

It will be understood that the various above described forms of the container in which the metal is treated for removing the zinc need not necessarily be of elemental carbon, and particularly the container shown by Figs. 10, 11 and 12, but in such cases with loss of the beneficial effects produced by the elemental carbon. Further, it will be understood that conditions in the furnace in which the metal is treated ordinarily will be suiiciently non-oxidizing Without entering an inert gas into the furnace, and, consequently, that such gas need not necessarily be employed. It will also be understood that, Within the scope of the appended claims, other and wide deviations may be made from the forms of the invention described without departing from the spirit of the invention.

I claim:

1. The method of removing zinc from copper base alloys which comprises heating a, body of the molten alloy having a free surface portion to at least the melting point of its non-zinciferous content under substantially non-oxidizing conditions in the presence of elemental carbon having an incandescent surface portion intersecting said free surface portion of the molten alloy, the residual amount of zinc in the molten metal from which it is so removed not exceeding 2. The method according to claim 1 in which the body of molten alloy is heated by radiation from an incandescent body or bodies positioned above its free surface portion.

3. The method of removing zinc frorn'copp'er base alloys which comprises heating a body of the molten alloy having a free surface portion to at least the melting point of its non-zinciferous content under substantially non-oxidizing conditions in a container the side wall surfaces of which in contact with the edges of the free surface portion of the metal comprise exposed elemental carbon heated to incandescence, the residual amount of zinc in the molten metal from which it is so removed not exceeding'10%.

4. The method according to claim 3 in which the body of molten alloy is heated by radiation from an incandescent body or bodies positioned above its free surface portion.

5. The method of removing zinc from copper base alloys which comprise heating a body of the molten alloy having a free surface portion to at lease the melting point of its non-Zinciferous content in a furnace chamber under substantially non-oxidizing conditions in the presence of elemental carbon, having an incandescent surface intersecting said free surface portion of the molten alloy, diluting the zinc vapors in contact with said free surface portion of the molten alloy with an inert gas, and discharging the dilute vapors from said chamber, the residual amount of zinc in the molten metal from which it is so removed not exceeding 10%.

6. The method of removing zinc from copper base alloys which comprises substantially continuously owing the molten alloy under non-oxidizing conditions through a container providing a relatively large free liquid surface in proportion to the volume of the alloy therein; providing elemental carbon presenting a surface intersecting said free surface; heating the alloy while in said container to at least the melting point of its non-zinciferous content, and simultaneously heating said elemental carbon to maintain it incandescent, the residual amount of Zinc in the molten metal from which it is so removed not exceeding 10%.

7. The method of removing zinc from copper base alloys which comprises substantially continuously iiowing the molten alloy under nonoxidizing conditions through a container providing a relatively large free liquid surface in proportion to the volume of the alloy therein; providing elemental carbon presenting a surface intersecting said free surface; heating the alloy while in said container to at least the melting point of its non-zinciferous content for evolving Zinc vapors from the alloy, and simultaneously heating said elemental carbon to maintain it incandescent; and discharging zinc vapors from a chamber in which said container is positioned without causing the zinc vapor evolved from the initial portions of the alloy being treated to contact with the free surface at the iinal portions of the alloy being treated; the residual amount of zinc in the molten metal from which it is so removed not exceeding 10%.

8. The method according to claim 7 in which an inert gas is swept over at least the final portions of the alloy being treated.

9. The method of recovering zinc from copper base alloys which comprises heating a body of the molten alloy having a free surface portion to at least the melting point of its non-zinciferous content under substantially non-oxidizing conditions in a furnace chamber and in the presence of incandescent elemental carbon having a surface intersecting said free surface portion of the molten alloy, and conducting the zinc vapors evolved in said chamber to a condenser maintained at such temperature as will .condense them to metallic zinc, the residual amount of zinc in the molten metal from Which it is so removed not exceeding 10%.

10. The method of recovering zinc from copper base alloys which comprises heating a body of the molten alloy having a free surface portion to at least the melting point of its non-zinciferous content in a furnace chamber under substantially non-oxidizing conditions in the presence of incandescent elemental carbon having a surface intersecting said free surface portion of the molten alloy, diluting the zinc vapors in contact with the surface of the molten alloy with an inert gas, and discharging the dilute vapors from said chamber to a condenser and therein condensing the zinc vapors to metallic zinc, the residual amount of zinc in the'molten metal from which it is so removed not exceeding 11. Apparatus for removing Zinc from Zinc bearing copper base alloy having, in combination, means .forming a substantially closed furnace chamber having a hearth, which hearth is formed at its upper side to provide a tortuous open channel for flow of the molten alloy on it, said channel comprising parallel passages extending transverselsr of the hearth connected in series at their end portions at leastadjacent their bottoms to cause the molten alloy to flow back and forth across the hearth, some at least of said passages being soconstructed as to cause portions of the alloy therein to be of greater depth than other portions therein, means for heating the molten alloy for evolving zinc'vapors therefrom, and said chamber having an opening for discharge of said vapors.

12. Apparatus for removing zinc from zinc bearing copper base alloy having, in combination, means forming a substantially closed furnace chamber having a hearth, w 'ch hearth is formed at its upper side to provide a tortuous open channel for ow of the molten alloy on it, said channel comprising parallel passages extending transversely of the hearth connected in series at their end portions at least adjacent their bottoms to cause the molten alloy to flow back and forth across the hearth, some at least of said passages having a submerged partition extending longitudinally thereof, means for heating the molten alloy for evolving zinc vapors therefrom, and said chamber having an opening for discharge of said vapors.

13. Apparatus for removing zinc from zinc bearing copper base alloy having, in combination, means forming a closed furnace chamber, a hearth of material of the group consisting of graphite and so-called carbon for receiving molten alloy, means formed of material of said group presenting a heat radiating surface above said hearth, electric resistance heating elements above said hearth arranged transversely thereof between it and said heat radiating surface, said hearth being formed at its upper side to provide a tortuous channel for the alloy flowing over it, which channel comprises parallel passages extending transversely of the hearth connected in series at their end portions adjacent their bottoms to cause the molten alloy to flow back and forth across the hearth in its passage over it, at least some of said passages being so constructed as to cause a material portion of the alloy therein to be of s'hallow depth, means forming a chamber for collecting the metal leaving said hearth, means for passing an inert gas over said hearth from adjacent its metal discharge end toward its opposite end having provision for bubbling at least a portion of said gas through the metal collected in said chamber, and means for discharging the mixture of said gas and zinc vapors from said chamber.

14. Apparatus for removing Zinc from zinc bearing copper base alloy having, in combination, means forming a substantially closed furnace chamber having a hearth, means for entering molten alloy on the hearth and flowing it continuously thereover in a stream, the upper side tion of flow of said alloy,

. means shaped to cause 18,. of which hearth is formed 'with metal contact-k ing'means shaped to' cause turbulence in said streamspaced electric resistance heating elements above the Vhearth arranged transversely of the general direction `of flow of alloyv from its l inlet to its discharge in respect to the hearth for heating theflowing alloyY for evolving zinc vapors therefrom, Ymeans having provision for flowing inert gas overthe hearth in contact with the alloy thereon counterto saidgeneral direcan'd'said chamber having an exit opening for said gas and the evolved zincvapors.

15. Apparatus forV removingyz'inc from zinc having, in combination,l means forming a. substantiallyclosed furnace bearing copper base alloy chamber having a hearth;'means for ventering moltenalloy on the hearth andflowing it continuously thereover in a stream, the upper side of which hearth is formed Awith alloy contacting turbulence in said stream,

spaced electric resistance heating elements above the hearth arranged transversely of the general direction of flow of alloyffrom its inlet to its discharge in Y respect to the hearth, and

means having provision'for flowing" an inert gasover the'hearthinr contact with the alloy thereon counter to said general direction of flow of said alloy and for bubbling at least part of the gas through the metal collected from the hearth prior to the gas passing over the hearth.

16. Apparatus for removing zinc from zinc bearing copper base alloy having, in combination, means forming a substantially closed furnace chamber having a hearth, means for entering molten alloy on said hearth and :owing it continuously thereover, spaced electric resistance heating elements above said hearth arranged transversely of the general direction of ow of alloy from its inlet to its discharge in respect to the hearth for heating such alloy and evolving zinc vapors therefrom, means for collecting metal discharged from the hearth, means providing for flow of inert gas over the hearth in contact with the alloy thereon counter to said general direction of flow of said alloy1 and for bubbling at least part of said gas through the collected metal prior to such gas passing over the hearth, the furnace chamber having an exit opening for said gas and evolved zinc vapors.

17. Apparatus for removing zinc from zinc bearing copper base alloy having, in combination, melting means for the alloy comprising a container provided with overflow means adapted to maintain a body of the molten alloy in the container, a second container for receiving the molten alloy overiiowing from the first mentioned container, means for heating the molten alloy in the second container for evolving zinc vapors therefrom, and means for controlling the rate of entering molten alloy into the second container comprising means for entering solid alloy into the first mentioned container for displacing molten alloy therein and causing the displaced molten alloy to pass through said overflow means.

18. Apparatus according to claim 1'7 in which the second container has provision for flowing the molten alloy through it in a stream, whereby the flow of said stream is controlled by the entering of solid alloy into the first mentioned container.

19. The method of recovering metallic zinc from copper base alloys which comprises heating a body of the molten alloy having a free surface portion to at least the melting point of its nonzinciferous content under substantially non-oxid'zingfoondipionsin aechamhenhayng.

of material presenting,elementalcarbon leated'to.v

incandescence interseotingfsaid, free. surface -por tion-to evolve zncvaporsiromothe alloy, the, residual amountof `zinlr; ingthemolten metal from- Which. it is so removedr noli:-fexceeding1 10% and.A

removing said vapors vfrorxnsad chamberand con-` densingfthem tov liquid 2mm 20. The method aocordngto, claim 19 in which side 219% REEEBENGES errno'.

The following. references are of# record/dn the 5 flle-of -thisjpatenta' the Vbody of mo1ten.a11y. is,heated -by heat ram dated froml incandesenfsurfaces abpvefthe free,

into thefrst mentiondfoontainer. mdY the surface ofV the `stream is maintained al: a, constant distanebelow said, ,ingle-en descent'.,surfaces.-`

ROLAND,`

Number 1,994,354' 1,994,358: 2,054,921,A 2,054,922 i 2,054,923?I UNITED STATES-PAIENTS I.

Name Date Soule. Oct. 3l, 1899; Mell'eni. May 19; 1914. Fulton July/29;. 1918) Thomsonn l Julyf 8,I 1919: Barnes' Sept. 7; 19263 Bunce et-zal: June;26; 1928. Isliker.- Ju1y,1,1193 0.t Ginder Mar. 1211935 Gindexzet-al.; Mar. 12, 1935, Holsteinl Mar; 12; 1935. Bettertonrn' Sept; 22; 198,62

Betterjton etal: Sept-2211936: Betterton,;et;;al.; Sepia-12,2, 19361 Perkns; Nom 17; 1936;'` Anderson. et: al: May 2, 1939; Anderson et al. Oct:,3,1. 1939:

Certificate of Correction Patent No. 2,429,584. October 21, 1947. FRANK F. POLAND It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 15, line 56, claim 1, strike out the Word portion column 16, line 5, claim 5, for comprise read comprises; line 10, same claim, after carbon strike out the comma; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflce.

Signed and sealed this 30th day of December, A. D. 1947.

THOMAS F. MURPHY,

Assistant (lommzsszoner of Patents. 

